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Let's say there is a multi-lens system of a converging lens (ex. a biconvex) and then a diverging lens with an object on the left of the system. And furthermore, let's say that due to the specific lenses, the diverging lens "creates" a virtual image to the left of the convex lens.

Why does that convex lens not re-transform the virtual image to a real image?

My thought is that the diverging lens is diverging the rays and not reflecting them back, but I fail to grasp the intuition of the real nature of the virtual image, and how it comes to exist, when thinking about such a system.

I have added a rough sketch of such a systementer image description here

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  • $\begingroup$ I'm not sure I'm following you correctly. Are you thinking that somehow the convex lens should "act" "twice"? That is it should affect the (imaginary) dashed line somehow? The fact is, once the light rays go through the first lens, then the first lens has done all it can do. That is, you can pretend that the first lens isn't there once you have the secondary rays leaving the first lens. The second lens is a diverging lens and so the light rays diverge, so they can be traced back to make the image. Can you clarify your misunderstanding? $\endgroup$
    – march
    Commented May 29 at 15:28
  • $\begingroup$ @march You've understood correctly. I might have over described my problem, however. What I'm trying to think about / understand is, how that post-divergence trace-back works. Edit: However, after thinking about it from the observer's perspective, I understand that I was thinking about it completely wrong and understand the premise better. $\endgroup$
    – Entangled Being
    Commented May 29 at 20:14

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Virtual rays are what-if scenarios invented by human beings. If you're ever confused just remember that your imagination has no power to influence the actual propagation of light.

In this example, the dotted line represents the fictional scenario that neither lens is present and the rays at the right come from the location of the virtual image. You could have instead drawn a dotted line that was focused by the convex lens and converged at a point nearer it. That would have represented the scenario that the convex lens is present but the concave lens is absent, and the rays at the right come from the then-appropriate virtual location. Both scenarios are potentially useful because they produce the same pattern of light at the far right, but neither one is true. There is no real image near the convex lens because there just isn't; the light doesn't converge there.

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If you see something, light rays spread out from it. Some reach your eye.

Light rays are spreading out from the concave lens. Some reach your eye. To your eye, this is the same as seeing something. But the point from which the spreading comes is behind the lens. The something is called a virtual image in this case.

Sometimes light rays converge after the last lens. They pass through a point and then diverge, reaching your eye. If the point from which they spread is on your side of the lens, the point is called a real image.

Either way, you just look at the diverging rays on your side of the last lens to find the location of the image. This is where the image appears to be.

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